This is a nationalization of PCT/NZ00/00139 filed Jul. 27, 2000 and published in English.
The invention relates to apparatus useful in a method of assessing pulp, paper or wood from the stem of a felled tree (e.g., so as to be determinate of possible destinies of logs to be cut from the stem), such as stiffness of sections of wood cut from the stem, or wood fibre characteristics such as fibre length or the strength of pulp produced from the wood.
The timber industry faces a need to efficiently utilise its rather variable forest resource. Timber classification, for example machine stress grading, is currently done at the end of the production chain. This process results in wastage from processing which ultimately proves to have been inappropriate. Clearly, it would be more efficient to measure log properties early in the chain and process the logs accordingly.
In our New Zealand Patent Specification Nos. 331527 (filed Aug. 1998) and NZ333434 filed Dec. 17, 1998 there are disclosed procedures in respect of the testing of felled tree stems or logs with a view to determining a destiny for that tree stem or log or logs to be cut from the tree stem.
New Zealand Patent Specification 331527 is directed to the selection of wood according to fibre characteristics so as to determine materials appropriate for the pulp and paper industry whilst, New Zealand Patent Application 333434 is directed to timber or lumber cutting determinations but with the prospects of directing inappropriate tree stems or logs to the pulp and paper industry.
The present invention is directed to apparatus sufficiently portable and effective in usage which will allow the adoption of such aforementioned methods in the field.
It is therefore an object of the present invention to provide such apparatus and the use of such apparatus in the field for such tree stem or log assessment purposes. As used herein MOE is the dynamic modulus of elasticity derived by the product of (A) the square of the velocity of an appropriate wave propagation between the ends of a felled tree stem or a log (V2) and (B) the specimen density xcfx81.
In one aspect the invention consists in an apparatus for providing an indicator of or from which stiffness can be estimated for elongate timber, logs or felled tree stems (hereafter xe2x80x9clogsxe2x80x9d) of known length L or measurable length L, said apparatus comprising or including
sensing means capable of being placed in contact with or in close proximity to a log end to detect the impulse and echoes thereof resulting from a striking of the other or that same log end,
processing means to derive using an echo or echoes sensed by said sensing means a said indicator, and
display means to display said indicator or any derivative thereof received from said processing means,
wherein said processing means tests algorithmically frequency transformed data derived from time based echo data with a view to deriving a measure or good estimate of fundamental frequency f0,
and wherein L is or can be entered into said processing means,
and wherein said processing means derives said indicator by reference to both f0 and L.
Preferably said processing means tests all spectral peaks of the echo data for membership of a series from which a best value of fundamental frequency f0 can be derived and related to the plane wave speed V and specimen length L by V=2L/f0 rather than by reliance on the identification of any single resonance peak.
Preferably said processing means recognises that the characteristic frequencies may be shifted significantly from a harmonic series f0, 2f0, 3f0. . . . . set and recognises that a better indication of the fundamental frequency f0, from which the speed V can be found is obtained from higher harmonics.
Preferably said processing means recognises that a better indication of the fundamental frequency f0 than an attempted direct measure of f0 itself is from at least the second harmonic.
Preferably said processing means recognises that whilst the natural resonance frequencies of stems and logs may be far from harmonic (principally on account of the asymmetry introduced by their taper or loading eg; when stacked) they may be transformed to a harmonic series by applying a correction which decreases as the harmonic number increases.
Preferably said processing means can transform observed resonant frequencies fn into multiples of a xe2x80x9ctruexe2x80x9d fundamental frequency f0 from which a plane wave velocity can be derived by reliance upon the relationship (fn=n f0)/fn=kcxe2x88x92n.
Preferably said the fractional deviation falls in geometric progression with ratio approximately 2.7.
Preferably the relationship is fn/nf0xe2x88x921=k/n2.
Preferably said processing means discriminates against noise spikes in the spectra, peaks from unwanted modes inadvertently excited, or any other signals which differ from the spectral peaks sought and which have the desired relationship by using a comb filter comprising a number of frequencies (xe2x80x9ccentrexe2x80x9d frequencies) which match the sought relationship, which can themselves be harmonic or have some other relationship, the comb filter having passbands wide enough to allow small derivations about each centre frequency.
forming the sum of the products of the actual spectral peaks and the comb filter, and
identifying as the sequence or filter which accounts for most spectral power, and, where necessary.
deciding between two filters which produce equal power sums on the basis of the comb which produces the least frequency offset between the actual spectral peaks and the filter centre frequencies.
Preferably said processing means uses such transforms to convert a harmonic series with a defined base frequency f0 to a non-harmonic series, thereby defining the centre frequencies of a comb filter with which the actual series may be compared, without the need for all members of the actual series to be present.
Preferably said processing means can calculate a confidence number to be displayed by said display means to indicate the likelihood that the indicated velocity is correct or whether a re-measure is advisable based on the amount of power in the spectral peak series identified with a base value off0, compared with spectral power not accounted for, e.g. that assumed to be in spurious noise spikes or non-longitudinal resonances inadvertently excited.
Preferably said indicator is V or V2 or a function of V or a function of V2.
Preferably said indicator is V2 or a function of V2 derived from a value or function of V, V having been determined by V=2L fn.
Preferably said display means displays V2 or an indicator or indicators of the one or more properties being assessed, such as MOE or an approximation of MOE derived from MOE=xcfx81V2 where xcfx81 has been approximated (e.g. as near 1000 kg/m3 for green felled logs).
Preferably said sensing means and/or processing means includes amplification means to ensure a sufficient gain to ensuing echoes in use.
Preferably said sensing means is adapted to be placed in contact with said log end.
Preferably said sensing means carries a switch for said processing means conducive, when activated, of good log/sensing means contact.
Preferably said sensing means is compliantly mounted by a sensing head to be physically pressed by a user against the log surface to be tested.
Preferably the compliant mounting of said sensing means within the means to be handled by a user i.e. the sensing head, is compliantly mounted by use of silicone rubber.
Preferably said sensing means is in a sensing head connected by flexible means to apparatus carrying said processing means and said display means.
Preferably said sensing means is or includes a piezo-style accelerometer.
Preferably said processing means has analog signal acquisition means, means for digitization and processing into a characteristic spectrum of the acquired analog signal data of the echoes and further software algorithms to interpret the data.
Preferably, with a view to power saving, said display means is a small low power display.
Preferably said sensing means is in a sensing head capable of one handed manipulation by a user and whereby the apparatus is adapted to minimise power consumption by allowing initiation of the measurement sequence by finger pressure on a push switch immediately prior to the striking of a log to be tested, such pressure on such a push switch encouraging positive contact between the head and the log surface.
Preferably said processing means is adapted to threshold the signal from said sensing means and immediately to apply an exponentially increasing amplification of the signal to compensate for absorption of the signal in the log so increasing the time over which acoustic signals can be useful digitalised and to increase spectral resolution.
Preferably the apparatus is such that power consumption is adapted to be minimised by allowing operation under the control of PLDs which remain in low current mode until enabled by an initiation switch after which there is a powering up, at least as needed, of analogue functions of said processing means with respect to signal acquisition, powering up and analysis of such signals and a sending results to the display means before being subsequently powered down after a time period or time periods.
Preferably there is provided a keyboard through which data entries can be made into said processing means.
Preferably preset information for data entry is selected from the class any one or more of
(i) velocity class codes e.g. colours to be painted on a log after its speed group is determined,
(ii) log length codes,
(iii) information analysis purposes,
(iv) information for instrument configuration purposes, and/or
(v) to control the sending of spectral information via a serial port to an external computer for graphical display or archiving.
Preferably, if desired, the apparatus can be externally controlled e.g. by connecting an external device via a serial port to the instrument power controllers and its microprocessor.
Preferably the apparatus has a hardware architecture substantially as herein described with reference to the accompanying drawings and which is operable in a manner substantially as herein described with reference to any one or more of the accompanying drawings.
Preferably said sensing means is adapted to be placed at or in close proximity to the same log end as that to be struck to provide said impulse.
In another aspect the invention is a method of providing an indicator of or from which stiffness, fibre characteristics or other properties can be estimated, which method involves an operative use of apparatus of the present invention.
Preferably said method is performed substantially as herein described with or without reference to any one of the accompanying drawings.
In still a further aspect the invention consists in a method of providing an indicator of or from which stiffness, fibre characteristics, or other properties can be estimated for a felled log of known or measurable length L, said method comprising or including the steps of
striking an end of the felled log whilst having sensing means of the previously defined apparatus in contact with or in close proximity to a log end to detect at least one echo of the impulse resulting from the striking of that same or the other log end,
processing the output of at least said sensing means in said processing means to derive, using an echo or echoes sensed by said sensing means, a said indicator, and
displaying on or by said display means said indicator or any derivative thereof received from said processing means,
optionally thereafter appropriately marking or otherwise indicating the fate of the log on the basis of the displayed indicator,
said process being further characterised in that said processing means tests frequency transformed data derived from time based echo data with a view to deriving a measure or good estimate of fundamental frequency f0, L is or can be entered into said processing means, and said processing means derives said indicator by reference to both f0 and L.
Preferably said indicator is an estimation of MOE for a green felled log on the basis of an estimation of its density at or about 1000 kg/m3.
In another aspect the invention is the use of apparatus of the present invention for use in a method of the present invention.
In still another aspect the invention is a method of generating and displaying an indicator of stiffness or fibre characteristics of wood within an elongate wooden structure (e.g. a log) which comprises or includes
(i) presenting an accelerometer based sensing means compliantly to an end of the elongate wooden structure,
(ii) impacting that said end of the structure so as to generate an impulse capable of reflection from the other end thereof,
(iii) passing the analogue signal detected by said compliant sensing means to a processing means,
(iv) processing the input data in said processing means to generate said indicator, and
(v) passing to the display means the generated indicator from said processing means for display,
wherein the architecture of the apparatus is such that said sensing means is a sensing head in which said accelerometer is compliantly mounted and is connected by a flexible link to a housing carrying said processing means and said display means.
Preferably said sensing head has a switch capable of being initiated by applying pressure which is conducive to compliant contact of said accelerometer with the end of said wooden structure.
Preferably said apparatus is apparatus as previously defined.
In another aspect the invention is a method of cutting a stem into logs of predicted speeds based upon the stem speed using the fact that the wave or acoustic speed along a stem has a characteristic variation by
(i) establishing an expression, the speed function, which represents the nature of the speed variation with distance along the stem, characteristic for a species and a locality, with one adjustable parameter to allow the variation along individual stems, to be matched,
(ii) measuring the average speed along the stem by a method as previously defined and converting this to a stem transit time,
(iii) integrating the wave travel time along the stem using the speed function, and altering the adjustable parameter until the integrated time equals the measured stem transit time, and
(iv) using the speed function thus established to compute the likely speed at points along the stem, to mark and route logs accordingly.
The present invention in another aspect consists in apparatus for providing an indicator of or from which stiffness can be estimated for a felled log of known length L or measurable length L, said apparatus comprising or including
sensing means capable of being placed in contact with a log end to detect the impulse and echoes thereof resulting from a striking of that same log end,
processing means to derive using an echo or echoes sensed by said sensing means a said indicator, and
display means to display said indicator or any derivative thereof received from said processing means,
wherein said processing means tests frequency transformed data derived from time based echo data with a view to deriving a measure or good estimate of fundamental frequency f0,
and wherein L is or can be entered into said processing means,
and wherein said processing means derives said indicator by reference to both f0 and L.
Preferably said indicator is V or V2 or a function of V or a function of V2.
Preferably said indicator is V2 or a function of V2 derived from a value or function of V, V having been determined by V=2L f0.
Preferably said display means displays V2 or an indicator or indicators of the one or more properties being assessed, such as MOE or an approximation of MOE derived from MOE=xcfx81V2 here xcfx81 has been approximated (e.g. as near 1000 kg/m3 for green felled logs).
Preferably said sensing means and/or processing means includes amplification means to ensure a sufficient gain to ensuing echoes (preferably logarithmic amplification of subsequent echoes).
Preferably said sensing means carries a switch conducive, when activated, of good log/sensor contact.
The present invention is reliant upon any of the processing procedures hereinafter described with or without reference to any one or more of the accompanying drawings and/or with or without reference to any of the algorithmic processes hereafter described.
Preferably the apparatus with a view to power savings in the field includes hardware incorporating analog signal acquisition means, means for digitization and processing into a characteristic spectrum of the acquired analog signal, further software algorithms to interpret the data, and preferably means to provide a small low power display rather than the full screen of a computer.
Preferably such display is of a MOE or wood fibre characteristics indicator.
Preferably said sensing head (preferably a piezo-style accelerometer) is compliantly mounted on a body, e.g.; using a pad of silicone rubber, and capable of being brought into contact with a tree stem end or log end.
Preferably said sensing head is flexibly connected to the processing means and display means.
Preferably said sensing head includes a test commencement switch or the like.
Preferably said sensing means is substantially as hereinafter described with reference to FIG. 1 of the accompanying drawings.
In a further aspect the present invention consists in a method of providing an indicator of or from which stiffness, fibre characteristics, or other properties can be estimated, which method involves an operative use of apparatus as previously set forth.
In still a further aspect the present invention consists in a method of providing an indicator of or from which stiffness, fibre characteristics, or other properties can be estimated for a felled log of known or measurable length L, said method comprising or including the steps of
striking an end of the felled log whilst having sensing means of the previously defined apparatus in contact with the log end to detect at least one echo of the impulse resulting from the striking of that same log end,
processing the output of at least said sensing means in said processing means to derive, using an echo or echoes sensed by said sensing means, a said indicator, and
displaying on or by said display means said indicator or any derivative thereof received from said processing means,
optionally thereafter appropriately marking or otherwise indicating the fate of the long on the basis of the displayed indicator,
said process being further characterised in that said processing means tests frequency transformed data derived from time based echo data with a view to deriving a measure or good estimate of fundamental frequency f0, L is or can be entered into said processing means, and said processing means derives said indicator by reference to both f0 and L.
Preferably said indicator is an estimation of MOE for a green felled log on the basis of an estimation of xcfx81=1000 kg/m3.